Tectonic Evolution Of Mesozoic Volcanic Basins In Western Liaoning And Northern Hebei

Famous by the "Jehol Biota", Northern Hebei and Western Liaoning is located in the northern North China plate, eastern Yanshan Orogenic Belt, extensively developed Mesozoic volcanic basins,its tectonic settings and evolution has been concerned for a long time. The author has collected some igneous rock and sedimentary samples in the J₂-K₁ formations from the Mesozoic Volcanic Basins in Northern Hebei and Western Liaoning province. Based on the characteristics of the major elements and trace elements, the author tries to explor the Mesozoic basins'tectonic setting and evolution of this area.By means of TAS classification, SiO₂-Nb/Y and SiO₂-K₂O illustrations, the author selected some contrast standards, then calssified the volcanic rocks. According to S. S. Sun and W. F. McDonough's established standard that published in 1989, the author has drawed some spider dirgrams and REE patterns.Northern Hebei and Western Liaoning igneous rocks were classified to High potassium calcium alkaline series and rhyolite. Major elements showed high content of SiO₂, Al₂O₃, K₂O, low Na₂O feature and pretty high content of Mg^#. Trace elements showed LREE strong enrichment, HREE strong deficit, weak Eu and Ce negative abnormal. Samples from Northern Hebei with high Sr and low Sr/Y ratios, showed no similarity to Adakite. While, samples with high Sr low Y from western Liaoning province showed similarity to Yanshanian volcanic rocks of eastern China, but has not gained any evidences to supporting crust thickening. The evidences showed that the igneous rocks in this area was caused by lower crust's partial melting and partially influenced by mantle material.During J₂-K₁, sufficient heat has been supplied to lower crust by mantle activities in this area and caused stretching and thinning, by which, a series of Mesozoic basins formed. A special LIP(Large Igneous Province) has formed by multistage magmatic activities that from different magma sources.